The act of cramming ones own feces into the complimentary hotel hair dryer so that the next unsuspecting person to use it gets a head full of brown highlights.
The hershey highlighter should only be used at seedy grungy hotels that you will not be returning to and at the same time encouraging the next guest to seek other hotels for future occasions.

"We were at this hotel and they didn't have kleenex beside the bed so I had to use toilet paper. So while I was in the bathroom getting toilet paper, I decided to create a mudblaster"